Final answer:
The incorrect statement about the BJT amplifier is that it has a relatively high input impedance. In reality, BJTs usually have lower input impedance than FETs. The other statements related to controlling output current and amplification factors are correct, while it's generally true that FETs are less susceptible to noise.
Step-by-step explanation:
Regarding the statements about a BJT (Bipolar Junction Transistor) amplifier, the incorrect statement is (b) The input impedance of a BJT amplifier is relatively high. BJTs typically have lower input impedance compared to FETs (Field-Effect Transistors). The input impedance of a transistor is important, especially in regards to how it will interact with the previous stage of the circuit.
On the other hand, statement (a) In BJT amplifier, input voltage VBE (base-emitter voltage) is used to control output current IC (collector current) for amplification operation is correct. This voltage acts as a valve, controlling the current from the emitter to the collector, thus allowing for amplification of signals, such as those from a microphone. This concept is demonstrated in audio amplification, where the base current, influenced by sound wave movements on a microphone diaphragm, controls a larger collector current that can then drive a loudspeaker.
Statement (c), The amplification factor of a BJT amplifier can be controlled by adjusting the base-emitter voltage, is also correct as altering the VBE can affect the transistor's operation and thus change the amplification. And (d) BJT amplifiers are less susceptible to noise compared to FET amplifiers is generally considered incorrect. FET amplifiers are known to have higher input impedance and lower noise levels, which is one of the reasons they are favored in certain applications over BJTs.